A ureteral stent is used to aid in transfer of urine from one of a patient's kidneys to the patient's bladder where obstructions or other conditions may inhibit normal flow, typically by creating a path around a blockage. While the stent is used to allow for free flow of urine, the stent itself should stay in place and not migrate out of or further into the kidney, or out of or further into the bladder.
In the past, ureteral stents consisted of hollow tubes having spirals or loops at both ends. The spirals caused both ends of the stent to deviate from a generally linear or tubular shape, forming structures that would less easily lead to migration of the stent. In addition, in these stents, urine would flow through the center of the tube, while the walls of the tube prevented obstructions from blocking the flow. These tubes often were designed to be as large as possible allow urine to flow more freely.
Attempts to modify the traditional tube design have included changing the shape of the ends of the stent in an attempt to even further inhibit migration.
Other attempts have involved replacing the bladder end of the stent with highly flexible strands or loops so as to reduce the size of the stent in the bladder end in an attempt to decrease the discomfort felt by a patient. In these designs, the stent may resemble a traditional tubular stent starting at the renal end and progressing for a significant distance, e.g., about 12 cm, or such a distance as to start the flexible strands or loops at about the iliac vessels of the patient. This significant distance was employed to further enhance migration of the stent. Stents of this type suffer from the problem that stents of multiple sizes must be created and then a physician must select what size stent to use based on approximations of the patient's physiology. In addition, even with the reduced size of the strands or loops, significant patient discomfort may result.
What is needed is a ureteral stent that overcomes the drawbacks described above.